Disruption of Core 1-mediated O-glycosylation oppositely regulates CD44 expression in human colon cancer cells and tumor-derived exosomes.

Aberrant O-glycosylation truncates O-glycans and is known to be closely associated with colorectal cancer (CRC), a major gastrointestinal tumor. CD44 is one of the highly post-transcriptionally modified O-glycoproteins participating in a series of physiological and pathobiological processes. In this research, we aimed to investigate whether CD44 expression in cells and exosomes can be influenced by disruption of Core 1-mediated O-glycosylation. Exosomes derived from LS174T and LSC human colon cancer cell lines were isolated from cell culture supernatant and pulled down using tetraspanin-specific antibody CD63 immunoaffinity magnetic beads. Identifications have been performed via transmission electron microscopy (TEM) and flow cytometry. CD63 immunoaffinity-purified exosomes are examined for CD44 expression by flow cytometric analyses. The percentages of CD44 in exosomes derived from abnormally O-glycosylated cells are significantly higher compared with those derived from normal ones, however, which is surprisingly contrary to the cellular expression levels of CD44. The secretion of truncated glycoproteins to the extracellular environment via microvesicles may be most likely its underlying mechanism. CD44 in exosomes might be a potential biomarker of aberrant O-glycosylation. This is the first study indicating that aberrant O-glycosylation can affect expression or delivery of O-glycoproteins via exosomes, which provides us some new sights in therapeutic strategies for human colon cancer.